Definition of D–day

  1. :  a day set for launching an operation; specifically :  June 6, 1944, on which Allied forces began the invasion of France in World War II

Origin and Etymology of d–day

D, abbreviation for day

First Known Use: 1918

D–DAY Defined for English Language Learners



Definition of D–day for English Language Learners

  • : a day on which something important is planned or expected to happen

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